This invention relates to a temperature control apparatus of an air conditioner for automobiles. More particularly, the invention relates to a temperature control apparatus applicable to an air conditioner for automobiles, which comprises a cooling unit disposed on an air passage and a heating unit disposed on the air passage downstream of the cooling unit, the amount of air passing through said heating unit being changeable by an air mix door, wherein the temperature in an automobile cab can be maintained at a desired level by changing the ratio of the amount of air passing through the cooling unit and heating unit to the amount of air passing through the cooling unit and bypassing the heating unit by means of said air mix door.
An air conditioner including a cooling unit and a heating unit having an air mix door which is disposed downstream of the cooling unit is known in the art and is generally called "re-heat air mix type conditioner."
Known methods for controlling the air mix door in this known apparatus are roughly divided into two types. According to one type, the temperature in an automobile cab is converted to an electric signal by means of a thermistor or the like, this signal is compared with the desired standard value, and a damper is actuated according to the deviation by electric means such as a solenoid or by converting the electric signal to a negative pressure. According to the other type, a sensor emitting a negative pressure signal according to the temperature in the cab is used, the output signal of the sensor is compared with the desired standard value and the air mix door is actuated by a negative pressure output according to the deviation.
These two methods, however, have the following defects.
In the former method, though an electric output can be obtained from the temperature sensor, since the output signal is very weak, provision of an amplifier is indispensable. Especially when the door is moved by a solenoid, the amplifying ratio should be drastically increased. When a solenoid is not used, provision of a electricity-negative pressure convertor is indispensable for converting the electric signal to a negative pressure, and the apparatus becomes expensive.
In the latter method, since an actuator is actuated by a negative pressure according to the negative pressure signal, a convertor or the like need not be provided but if the frictional resistance to sliding is changed in the door operated by the actuator, an error is caused in the displacement of the door and it is difficult to control the temperature to a desired level precisely. Since the air conditioner for an automobile is attached in a narrow space and it is used under violent vibration, the frictional resistance is readily changed in the portion of a rotary shaft and hence, the control reliability is very low.